class entry:
    
    class lvalue:
        def __init__(self, scope, rname):
            self._scope = scope
            self._rname = rname
        def get(self):
            return self._scope.get(self._rname, None)
        def set(self, value):
            self._scope[self._rname] = value

    def incoming(self, event):
        temporal, node = event.data
        if temporal == "post":
            event.trail.operands.append(self.lvalue(event.trail.vars, node.ref.name))
